Electric motor with a housing for at least two carbon brushes

ABSTRACT

An electric motor includes carbon brushes ( 5 ) disposed in a holder ( 6 ) that are pressed by means of a spring force ( 7 ) in a radial direction against a jacket face of a cylindrical collector ( 4 ) that is fixed to an armature shaft ( 2 ) of the motor. The holder ( 6 ) for the carbon brushes ( 5 ) can be removed from the motor with little effort as a result of a provision of covering means ( 11, 12 ) that cover a pivot bearing ( 3 ) of the armature shaft ( 2 ) to protect it against the entry of dirt on a side of the covering means ( 11, 12 ) facing the holder ( 6 ) for the carbon brushes ( 5 ), provided with one or more chamfers ( 14, 15 ) in such a way that the carbon brushes ( 5 ) slide over the covering means ( 11, 12 ) as the holder ( 6 ) is being pulled off and that the carbon brushes ( 5 ) thereby are thrust radially outward counter to the spring force ( 7 ).

PRIOR ART

The present invention relates to an electric motor with a holder for atleast two carbon brushes, which are pressed by spring force in theradial direction against the jacket face of a cylindrical collectorfixed to the armature shaft of the motor.

Mechanically commutated electric motors typically have a carbon brushcontact, of the kind also described for instance in German PatentApplication 101 53 574.0, which was not yet published by the prioritydate of the present application. In this application cited, whosesubject is the rotatable bearing of the holder for the carbon brushes,no provisions that make it as simple as possible to change carbonbrushes are disclosed. The carbon brushes of an electric motor, whichare exposed to wear, must be replaced after a certain number of hours ofoperation. Such a change of carbon brushes is often impossible becauseof tight space conditions in the surroundings of the electric motor,such as in power tools. Therefore the entire holder of the carbonbrushes must often be removed so that the carbon brushes can be replacedoutside the device. It is therefore the object of the invention todisclose an electric motor of the type defined at the outset in whichthe holder for the carbon brushes can be removed as simply as possible.

ADVANTAGES OF THE INVENTION

The aforementioned object is attained with the characteristics of claim1, in that the holder with the carbon brushes can be pulled off thecollector in the axial direction of the armature shaft by way of a pivotbearing that holds the armature shaft, and that means which cover thepivot bearing against the entry of dirt are provided, on their sidetoward the holder with the carbon brushes, with one or more chamfersthat extend in such a way that the carbon brushes slide over it as theholder is being pulled off and in the process are thrust radiallyoutward counter to the spring force.

Despite means that protect the pivot bearing against the entry of dirt(such as material abraded from the carbon brushes, or drillings), theinvention makes simple removal of the holder with the carbon brushespossible.

Advantageous refinements of the invention are disclosed in the dependentclaims.

To protect the pivot bearing against becoming soiled, an armature diskmay be disposed between the pivot bearing and the collector, and/or abearing dome may be placed on the pivot bearing. Unhindered pulling offof the holder with the carbon brushes over the pivot bearing is madepossible by providing that the side of the armature disk and/or of thebearing dome oriented toward the collector is provided with a chamferextending rectilinearly or in curved form.

DRAWING

The invention is described in further detail below in conjunction withtwo exemplary embodiments shown in the drawing. Shown are:

FIG. 1 a is a fragmentary longitudinal section through an electricmotor, with a carbon brush holder disposed on its collector and withmeans of a first embodiment for protecting the armature shaft pivotbearing from soiling; FIG. 1 b is a magnified portion of the fragmentarylongitudinal section depicted in FIG. 1 a;

FIGS. 2 a-1 through 2 e-1 depict various positions of a carbon brush asthe holder for the carbon brushes is being pulled off from the armatureshaft of the motor;

FIGS. 2 a-2 through 2 e-2 depict magnified portions of the variouspositions depicted in FIGS. 2 a-1 through 2 e-1, respectively;

FIG. 3 a depicts a fragmentary longitudinal section through an electricmotor, with a carbon brush holder disposed on its collector and withmeans of a second embodiment for protecting the armature shaft pivotbearing from soiling; and

FIG. 3 b is a magnified portion of the FIG. 3 a fragmentary longitudinalsection.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

In FIG. 1 a, a portion of an electric motor of the kind used preferablyin hand-operated electrical tools, is shown. Since the motor isconstructed rotationally symmetrically with respect to its longitudinalaxis, only half of the electric motor is shown in FIG. 1 a. In a knownmanner, the motor has a rotatable armature 1, whose armature shaft, onits end remote from the armature 1, is supported in a pivot bearing 3. Acylindrical collector 4 which rotates with the armature shaft 2 isdisposed on the armature shaft 2, between the armature 1 and the pivotbearing 3 for the armature shaft 2. The collector 4 is provided withelectrical contact by at least two carbon brushes, of which only onecarbon brush 5 is shown in the sectional view in FIG. 1 a. The carbonbrushes have the function of establishing an electrical connection froman external power connection to the collector of the motor. The carbonbrushes 5 are disposed in a holder 6 and are pressed by a spring forcein the radial direction against the jacket face of the cylindricalcollector 4. The spring force is exerted by a spring 7, which rests onthe face end, remote from the collector 4, of the carbon brushes 5 andexerts a contact pressure in the direction of the jacket face of thecollector 4. The holder 6 for the carbon brushes 5 is releasably fixedto the housing 8 of the motor. The releasable fixation is preferablyeffected by means of a detent element 9, which is present in the holder6 and can be snapped into the housing 8. A special receptacle chamber10, into which the holder 6 for the carbon brushes 5 is insertable, maybe integrally formed onto the housing 8.

An armature disk 11 is disposed on the armature shaft 2, between thecollector 4 and the pivot bearing 3. This armature disk 11 serves toprotect the pivot bearing 3 for the armature shaft 2 against the entryof material abraded from the carbon brushes 5 as well as from particles(such as drilling dust and drillings), which are aspirated in theprocess of operating an electrical power tool. This armature disk 11 hasa larger diameter than the collector 4 and therefore protrudes radiallypast the collector 4, as is readily apparent from the magnified portionof the FIG. 1 a fragmentary longitudinal section that is depicted inFIG. 1 b.

As a rule, the pivot bearing 3 of a motor is covered by a bearing dome12. The bearing dome 12 is a caplike structure, communicating with thehousing 8, which covers the pivot bearing 3 and the armature shaft,placed in the pivot bearing, on the face end remote from the collectorand which, with a preferably flattened, cylindrical wall 13, coaxiallysurrounds the pivot bearing 3.

As already described above, the holder 6 with the carbon brushes 5 isreleasably secured to the housing 8. If the holder 6 is to be removedfrom the motor so that the carbon brushes can be changed, then thedetent element 9 of the holder 6 is released, and the holder is pulledoff the collector 4 in the axial direction (direction of the arrow X) ofthe armature shaft 2. In FIGS. 2 a-1 through 2 e-1, five differentpositions of the carbon brush 5 are shown during the process of pullingoff the holder 6 for the carbon brushes 5. For the sake of simplicity,each of the FIGS. 2 a-1 through 2 e-1 shows only one carbon brush 5 withthe spring 7 holding it down, without the holder 6. FIGS. 2 a-2 through2 e-2 depict magnified portions of the various positions depicted inFIGS. 2 a-1 through 2 e-1, respectively.

In the view shown in FIGS. 2 a-1 and 2 a-2, the holder is moved in theaxial direction, so that the brushes 5 slide over the collector 4 in thedirection of the armature disk 11. Finally, the carbon brushes 5 meetthe armature disk 11, which protrudes radially past the collector 4.This situation is shown in FIGS. 2 b-1 and 2 b-2. Because of the largerdiameter of the armature disk 11 in comparison with the collector 4,this would prevent the holder 6 with the carbon brushes 5 from beingpulled farther in the X direction and thus from being removed entirelyfrom the motor. Because the armature disk 11, on its side toward thecarbon brushes 5, is provided with a chamfer 14, which decreases fromthe outer diameter of the armature disk 11 to the carbon brushes 5, thecarbon brushes slide along this chamfer 14 over the armature disk 11,and in the process the carbon brushes 5 are thrust radially outwardcounter to the force of the spring 7.

The enlarged details of the magnified portions shown in FIGS. 2 a-2through 2 e-2 depict the position of the carbon brushes 5 relative tothe armature disk 11 and to the bearing dome 12. FIGS. 2 c-1 and 2 c-2show the position of the carbon brushes 5 once they have been slippedover the chamfer 14 of the armature disk 11 as far as the outermostpoint of the armature disk 11. After a further forward motion in the Xdirection of the holder 6 with the carbon brushes 5, the carbon brushesslide over the topmost point of the armature disk 11, until they meetthe bearing dome 12. This situation is shown in FIGS. 2 d-1 and 2 d-2.The bearing dome 12, or more specifically the face end toward the carbonbrushes 5 of the cylindrical wall 13 of the bearing dome 12, is likewiseprovided with a chamfer 15. This chamfer of the bearing dome 12decreases in diameter from the outermost diameter of the cylindricalwall 13 in the direction of the carbon brushes 5. Thus even a bearingdome 12 that has a somewhat larger diameter than the armature disk 11 isno hindrance to the continued motion of the holder 6 with the carbonbrushes 5. That is, the carbon brushes 5 slide over the chamfer 15 ofthe bearing dome and are thrust outward, counter to the force of thespring 7, until the carbon brushes 5 finally rest on the surface of thecylindrical wall 13 of the bearing dome 12. Finally, the holder 6 withthe carbon brushes 5 disposed in it can be pulled all the way off, overthe surface of the cylindrical wall 13 of the bearing dome 12. Thechamfers 14 and 15 on the armature disk 11 and bearing dome 12 canextend rectilinearly, as shown in the drawings, or can have a curvedcourse.

So that it is also possible to slip the holder 6 with the carbon brushes5 on over the armature disk 11 as far as the collector 4 withouthindrance, as well, the armature disk 11 is provided, on its side towardthe bearing dome 12, with a chamfer 16, which enables the carbon brushes5 to be thrust without hindrance from the bearing dome 12 over thearmature disk 11 onto the collector 4. This chamfer 16 on the armaturedisk 11 is actually required only whenever the outer diameter of thebearing dome 12 is less than the outer diameter of the armature disk 11.This is because only for that case would the armature disk 11 be ahindrance as the holder 6, with the carbon brushes 5, is being slippedon in the direction of the collector 4.

In a departure from the exemplary embodiment described above, it ispossible for only an armature disk 11 or only a bearing dome 12 to beprovided for protecting the pivot bearing 3. In that case, only onechamfer 14 or 15, on the armature disk 11 or on the bearing dome 12,respectively, is necessary.

The exemplary embodiment shown in FIG. 3 a, including a magnifiedportion shown in FIG. 3 b, differs from the exemplary embodiments shownin FIGS. 1 a, 1 b, and 2 a-1, 2 a-2 through 2 e-1. 2 e-2 only in thedesign of the means that protect the pivot bearing 3 against dirt. Allthe other details of the exemplary embodiment in FIGS. 3 a, 3 bcorrespond to those of the exemplary embodiment of FIGS. 1 a, 1 b, and 2a-1, 2 a-2 through 2 e-1. 2 e-2 and are identified by the same referencenumerals. In the exemplary embodiment of FIGS. 3 a and 3 b, the bearingdome 12 protrudes, with its cylindrical wall 131, axially in thedirection of the collector 4, past the armature disk 11. A chamfer 15over which the holder 6 can slide is therefore required only on the faceend of the cylindrical wall 131 of the bearing dome 12 oriented towardthe holder 6 having the carbon brushes 5.

The wall 131 of the bearing dome 12, which wall extends in the axialdirection and protrudes past the armature disk 11, moreover has theadvantage that the gap between it and the armature disk 11 can be keptquite small, which leads to increased leakproofness of the pivot bearing3. The elongation of the cylindrical wall 131 in the direction of thecollector 4 has the effect of carrying cooling air directly to thecollector 4 and to the carbon brushes 5.

1. An electric motor comprising a holder (6) for at least two carbonbrushes (5), which by means of a spring force (7) are pressed in aradial direction against a jacket face of a cylindrical collector (4)fixed to an armature shaft (2) of the motor, and a pivot bearing (3)that holds the armature shaft (2), characterized in that the holder (6)can be pulled off together with the carbon brushes (5) from thecollector (4) in the axial direction of the armature shaft (2); and thatcovering means (11, 12) for covering the pivot bearing (3) to protect itagainst entry of dirt are disposed on a side of the covering means (11,12) facing the holder (6) for the carbon brushes (5), provided with oneor more chamfers (14, 15) in such a way that the carbon brushes (5)slide over the covering means (11, 12) as the holder (6) is being pulledoff and that the carbon brushes (5) thereby are thrust radially outwardcounter to the spring force (7).
 2. The electric motor of claim 1,characterized in that disposed between the collector (4) and the pivotbearing (3) on the armature shaft (2) is an armature disk (11); and thatan end of the armature disk (11) protruding radially past the collector(4) is provided with a chamfer (14), over which the carbon brushes (5)slide as the holder (6) is being pulled off and thereby are thrustradially outward counter to the spring force (7).
 3. The electric motorof claim 1, characterized in that the pivot bearing (3) is covered by abearing dome (12), which on its face end toward the holder (6) for thecarbon brushes (5) is provided with a chamfer (15), over which thecarbon brushes (5) slide as the holder (6) is being pulled off and inthe process are thrust radially outward counter to the spring force (7).4. The electric motor of claim 1, characterized in that disposed betweenthe collector (4) and the pivot bearing (3) on the armature shaft (2) isan armature disk (11); that the pivot bearing (3) is covered by abearing dome (12), which protrudes past the armature disk (11) in thedirection of the collector (4); and that the bearing dome (12), on itsface end toward the holder (6) for the carbon brushes (5), is providedwith a chamfer (15), over which the carbon brushes (5) slide as theholder (6) is being pulled off and in the process are thrust radiallyoutward counter to the spring force (7).
 5. The electric motor of one ofclaim 2, characterized in that the chamfer (14, 15) extendsrectilinearly.